1. Field of the Invention
The present invention is directed to a method of improving semiconductor matter and, more particularly, to a method of engineering minority carrier lifetime in silicon material as needed for in the fabrication of high density Very Large Scale Integration (VLSI) semiconductor devices and high performance solar cells.
2. Description of the Prior Art
Increasing the lifetime of minority carriers in Silicon material used for fabricating semiconductor VLSI devices such as high density memories or high performance solar cells is of paramount importance. As is also appreciated, increased minority carrier lifetime, hereafter also referred to as increased lifetime, is achievable by gathering impurities in the semiconductor material to defective points in such material. This process is called `gettering`. To improve the material, it is necessary to getter the impurities away from the surface of the material where the active circuits are fabricated. As used in the art and herein, impurities refer to foreign atoms or bodies in a layer of material, while defects relate to distortion of the crystaline lattice symmetry of the material.
Heretofore, it has been suggested that increased lifetime in a surface layer can be achieved by purposely damaging the bottom side of a semiconductor material, such as silicon, and subsequently annealing the silicon material. Although it is claimed that increased lifetime is achieved, the need to purposely damage the crystal is highly undesirable and the resulting increased lifetime is limited for the following reasons.
The extent and distribution of damage, introduced in one wafer, cannot be duplicated in other wafers. Thus, the increased lifetime is not reproducible. Also, due to the thickness of the wafer, or crystal, relatively extensive damage must be induced. Quite often, the damage, which is intentionally produced at the wafer's bottom side, extends to the top surface or close to it, thereby destroying the usefulness of the gettering process. Furthermore, the damage in the crystal is typically not uniform and therefore, the increased lifetime at the surface is highly irregular on a microscopic scale which is most undesirable.